CR3.6

Hydrology of ice shelves, ice sheets and glaciers - from the surface to the base

Dynamic subglacial and supraglacial water networks play a key role in the flow and stability of ice sheets. The accumulation of meltwater on the surface of ice shelves has been hypothesized as a potential mechanism controlling ice-shelf stability, with ice-shelf collapse triggering substantial increases in discharge of grounded ice. Observations and modelling also suggest that complex hydrological networks occur at the base of glaciers and these systems play a prominent role in controlling the flow of grounded ice. This session tackles the urgent need to better understand the fundamental processes involved in glacial hydrology that need to be addressed in order to accurately predict future ice-sheet evolution and mass loss, and ultimately the contribution to sea-level rise .

We seek contributions from both the modelling and observational communities relating to any area of ice-sheet hydrology. This includes but is not limited to: surface hydrology, melt lake and river formation; meltwater processes within the ice and firn; basal hydrology; subglacial lakes; impacts of meltwater on ice-sheet stability and flow; incorporation of any of these processes into large-scale climate and ice-sheet models.

Co-organized by HS13
Convener: Sammie BuzzardECSECS | Co-conveners: Ian Hewitt, Amber Leeson, Martin WearingECSECS
vPICO presentations
| Tue, 27 Apr, 09:00–10:30 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Sammie Buzzard, Ian Hewitt, Amber Leeson
09:00–09:02
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EGU21-508
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ECS
Mariel Dirscherl, Andreas Dietz, Celia Baumhoer, Christof Kneisel, and Claudia Kuenzer

Supraglacial meltwater accumulation on ice sheets and ice shelves can have considerable impact on ice discharge, mass balance and global sea-level-rise. With further increasing surface air temperatures, surface melting and resulting processes including hydrofracturing, meltwater penetration to the glacier bed as well as surface runoff will cumulate and most likely trigger unprecedented ice mass loss from the Greenland and Antarctic ice sheets. To date, the Antarctic surface hydrological network remains understudied calling for increased monitoring efforts and circum-Antarctic mapping strategies. This is particularly important given that Antarctica’s future contribution to global sea-level-rise is the largest uncertainty in current projections.

In this study, we present a novel methodology for Antarctic supraglacial lake extent mapping in Sentinel-1 Synthetic Aperture Radar imagery using state-of-the-art deep learning techniques. The method was implemented with the aim of complementing a previously developed supraglacial lake detection algorithm applying Machine Learning on optical Sentinel-2 data in order to deliver a more complete picture of Antarctic meltwater ponding compared to single-sensor mapping products. The deep learning model was trained on 21,200 Sentinel-1 image patches using a modified ResUNet for semantic segmentation of supraglacial lakes and evaluated by means of ten spatially or temporally independent Sentinel-1 test acquisitions distributed across the Antarctic continent. Besides, George VI Ice Shelf is analyzed for intra-annual lake dynamics throughout austral summer 2019/2020 and decision-level fused Sentinel-1 and Sentinel-2 maximum lake extent mapping products are presented for selected time periods. Future work involves the integration of more training data as well as the generation of circum-Antarctic mapping products using both, Sentinel-2 and Sentinel-1 derived lake extent mappings. These will be crucial for intra-annual analyses on supraglacial lake occurrence across the whole continent and associated drivers and impacts.

How to cite: Dirscherl, M., Dietz, A., Baumhoer, C., Kneisel, C., and Kuenzer, C.: A novel technique for automated mapping of Antarctic supraglacial lakes in Sentinel-1 SAR imagery using deep learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-508, https://doi.org/10.5194/egusphere-egu21-508, 2021.

09:02–09:04
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EGU21-2798
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ECS
Lauren Rawlins, David Rippin, Andrew Sole, Stephen Livingstone, and Kang Yang

Throughout the satellite era, an increasingly positive trend in the extent and duration of seasonal surface melt has been observed across the Greenland Ice Sheet (GrIS). Surface melt, and meltwater runoff now accounts for over half of GrIS mass loss annually, signifying the importance of surface mass balance on the future contribution to global sea level rise. A vast expanse of supraglacial channel networks and lakes now dominate the ablation zone during the melt season, transporting, storing, and evacuating increasingly large volumes of meltwater from the ice surface. The interception of this water, either by moulins or through linked crevasses, can propagate through the ice column and flood the ice-bed interface, influencing ice velocity and, in turn ice discharge over the grounding line.

To date, much of the hydrological interest on the GrIS has centred around its western and south-western margins, often limited to short windows (days) during the melt season. This study expands surface hydrological mapping to other regions of the GrIS, specifically its northern sector, and explores network evolution across both seasonal (intra-) and inter-annual timescales.

This study utilises a satellite-derived Normalised Difference Water Index (NDWI) alongside an automatic river detection algorithm to effectively delineate active supraglacial channel networks and (hydrologically-connected) saturated slush zones using Sentinel-2 and Landsat optical imagery. This work reveals a transformation of the northern supraglacial channel network from a highly-fragmented system of short channels extending a maximum of ~40 km inland during the 1980’s, to one dominated by long, parallel channels extending ~80 km inland from 2016. The observations presented in this study have significant implications on both the speed and efficiency of supraglacial meltwater drainage of the GrIS, holding a great potential to impact the dynamic response of outlet glaciers, and ice sheet mass loss.

How to cite: Rawlins, L., Rippin, D., Sole, A., Livingstone, S., and Yang, K.: Rivers on Ice: The Evolution of Supraglacial Channels on the Greenland Ice Sheet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2798, https://doi.org/10.5194/egusphere-egu21-2798, 2021.

09:04–09:06
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EGU21-3625
Ya Li, Kang Yang, Laurence Smith, Xavier Fettweis, Shuai Gao, and Wensong Zhang

Large, complex supraglacial river networks are widely distributed on the northwestern Greenland Ice Sheet (GrIS) each summer. Owing to the absence of moulins and crevasses on the ice surface, meltwater is continuously routed on the ice surface by supraglacial river networks to feed proglacial rivers on land. This continuous supraglacial-proglacial river system controls the magnitude and timing of surface meltwater runoff on the northwestern GrIS but remains poorly studied. In this study, we first mapped the supraglacial-proglacial river system across the Inglefield Land on the northwestern GrIS during 2016–2019 melt seasons using ninety Sentinel-2 and forty-five Landsat-8 images. Then, we proposed two quantitative river metrics, i.e., surface meltwater area fraction and proglacial river width, to quantify the seasonal and annual evolutions of the supraglacial-proglacial river system. Next, we correlated these satellite-derived river metrics with surface meltwater runoff estimated by two Surface Mass Balance (SMB) models (MAR v3.11 and MERRA-2), and estimated the optimal meltwater routing lag times. Our results showed that: (1) two satellite-derived river metrics, surface meltwater area fraction and proglacial river width, are strongly and positively correlated, indicating that the northwestern GrIS supraglacial-proglacial river system can efficiently route surface meltwater from the ice surface to the proglacial zone; (2) these two satellite-derived river metrics are also positively correlated with simultaneous surface runoff simulated by MAR and MERRA-2, indicating that SMB models can capture the general runoff pattern but exhibit considerable discrepancy with satellite observations; and (3) delayed MAR surface runoff better match two satellite-derived river metrics than simultaneous MAR surface runoff, and the optimal lag times are both two days, suggesting that supraglacial routing accounts for most of the lag time whereas rapid proglacial routing accounts for short lag time. Overall, the northwestern GrIS supraglacial-proglacial river system is a unique and efficient meltwater routing system, and multi-temporal satellite observations of this river system raise prospects for directly estimating surface meltwater runoff on the poorly-studied northwestern GrIS.

How to cite: Li, Y., Yang, K., Smith, L., Fettweis, X., Gao, S., and Zhang, W.: Surface meltwater routing through the supraglacial-proglacial river system on the northwestern Greenland Ice Sheet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3625, https://doi.org/10.5194/egusphere-egu21-3625, 2021.

09:06–09:08
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EGU21-6263
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ECS
Jennifer Arthur, Chris Stokes, Stewart Jamieson, Rachel Carr, and Amber Leeson

Surface meltwater ponding can weaken and trigger the rapid disintegration of Antarctic ice shelves which buttress the ice sheet, causing ice flow acceleration and global sea-level rise. While supraglacial lakes (SGLs) are relatively well documented during some years and selected ice shelves in Antarctica, we have little understanding of how Antarctic-wide SGL coverage varies between melt seasons. Here, we present a record of SGL evolution around the peak of the melt season on the East Antarctic Ice Sheet (EAIS) over seven consecutive years. Our findings are based on a threshold-based algorithm applied to 2175 Landsat 8 images during the month of January from 2014 to 2020. We find that EAIS-wide SGL volume fluctuates inter-annually by up to ~80%. Moreover, patterns within regions and on neighbouring ice shelves are not necessarily synchronous. Over the whole EAIS, total SGL volume was greatest in January 2017, dominated by the Amery and Roi Baudouin ice shelves, and lowest in January 2016. Excluding these two ice shelves, SGL volume peaked in January 2020. Preliminary results suggest EAIS-wide total SGL volume and extent are weakly correlated with firn model simulations of firn air content, surface melt and minimum ice lens depth predicted by the regional climate model MAR. On certain ice shelves, years with peak SGL volume correspond with minimum firn air content. This work provides important constraints for numerical ice-shelf and ice-sheet model predictions of future Antarctic surface meltwater distributions and the potential impact on ice-sheet stability and flow.  

How to cite: Arthur, J., Stokes, C., Jamieson, S., Carr, R., and Leeson, A.: Inter-annual variability in supraglacial lakes around East Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6263, https://doi.org/10.5194/egusphere-egu21-6263, 2021.

09:08–09:10
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EGU21-7304
Nanna Bjørnholt Karlsson, Anne M Solgaard, Kenneth D Mankoff, Fabien Gillet-Chaulet, Joseph A. MacGregor, Douglas I. Benn, Ian Hewitt, and Robert S. Fausto

The total mass balance of ice sheets is determined using estimates of ice volume change from satellite altimetry, measurements of gravity changes, or by differencing solid ice discharge and surface mass balance. The basal melt is only implicitly included in the first two and entirely neglected by the last method. Here, we show that the basal mass loss of the Greenland Ice Sheet is a non-negligible component of the total mass budget. We estimate that the basal melt is 21.4 +4.4/-4.0 Gt per year corresponding to 8% of the ice sheet’s total mass balance. The basal melt is composed of three separate terms; melt caused by frictional heat, geothermal heat and heat from surface meltwater, respectively, and the basal friction term is responsible for half of the basal melt.

Importantly, the geothermal and friction heat are active year round. This implies that a quantifiable volume of freshwater is discharged into the Greenlandic fjords during the winter where the ice-fjord interactions often are assumed dormant. Here, we present basal melt volumes from different outlet glaciers that discharge into Greenlandic fjords. We compare the basal melt to the freshwater volumes generated by surface meltwater, and identify locations where basal melt volumes are comparable to surface meltwater during the winter.

How to cite: Karlsson, N. B., Solgaard, A. M., Mankoff, K. D., Gillet-Chaulet, F., MacGregor, J. A., Benn, D. I., Hewitt, I., and Fausto, R. S.: Subglacial Discharge of the Greenland Ice Sheet from Basal Melt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7304, https://doi.org/10.5194/egusphere-egu21-7304, 2021.

09:10–09:12
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EGU21-7431
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ECS
Peter Tuckett, Jeremy Ely, Andrew Sole, Stephen Livingstone, and James Lea

Surface meltwater is widespread around the margin of the Antarctic Ice Sheet during the austral summer. This meltwater, typically transported via surface streams and rivers and stored in supraglacial lakes, has the potential to influence ice-sheet mass balance through ice-dynamic and albedo feedbacks. To predict the impact that surface melt will have on mass balance over coming decades, it is important to understand spatial and temporal variability in surface meltwater extent. A variety of methods have been used to detect supraglacial lakes in Antarctica, yet a multi-annual, continent-wide study of Antarctic supraglacial meltwater has yet to be conducted. Cloud-based computational platforms, such as Google Earth Engine (GEE), enable large-scale temporal and spatial analysis of remote sensing datasets at minimal time expense. Here, we implement an automated method for meltwater detection in GEE to generate continent-wide, bimonthly repeat assessments of supraglacial lake extent between 2013 and 2020. We use a band-threshold based approach to delineate surface water from Landsat-8 imagery. Furthermore, our method incorporates a novel technique for quantifying meltwater extent that accounts for variability in optical image coverage and cloud cover, enabling an upper uncertainty bound to be attached to minimum mapped lake areas. We present results from continent-wide mapping, and highlight initial findings that indicate evolution of lakes in Antarctica over the past seven years. This work demonstrates how platforms such as GEE have revolutionized our ability to undertake large-scale projects from remote sensing datasets, allowing for greater temporal and spatial analysis of cryospheric processes than previously possible.

How to cite: Tuckett, P., Ely, J., Sole, A., Livingstone, S., and Lea, J.: Continent-wide bimonthly mapping of Antarctic surface meltwater using Google Earth Engine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7431, https://doi.org/10.5194/egusphere-egu21-7431, 2021.

09:12–09:14
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EGU21-8080
Shelley MacDonell, Francisco Fernandoy, Paula Villar, and Arno Hammann

In recent decades, several large ice shelves in the Antarctic Peninsula region have experienced significant ice loss, likely driven by a combination of oceanic, atmospheric and hydrological processes. Of these three, the role of liquid water on and in ice shelves is the lesser defined variable, largely due to the paucity of field measurements. Even though the hydrological system is largely unknown, several authors have proposed the existence of firn aquifers on Antarctic ice shelves, however little is known about their distribution, formation, extension and role in ice shelf mechanics. In this study we present the discovery of saturated firn at three drill sites distributed across the Müller ice shelf (67º 14’S; 66º52’W) (one near the front and two in the central region of the ice shelf), which leads us to the conclusion of at least one large firn aquifer or disconnected smaller firn aquifers on this ice shelf. From the stratigraphic analysis of three short firn cores extracted during February 2019 we describe a new classification system to identify the structures and morphological signatures of refrozen meltwater, identify evidence of superficial meltwater percolation, and use this information to propose a conceptual model of firn aquifer development on the Müller ice shelf. The detailed stratigraphic analysis of the sampled cores will provide an invaluable baseline for modelling studies.

How to cite: MacDonell, S., Fernandoy, F., Villar, P., and Hammann, A.: Stratigraphic analysis of firn cores from the Müller Ice Shelf, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8080, https://doi.org/10.5194/egusphere-egu21-8080, 2021.

09:14–09:16
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EGU21-10388
Bert Wouters and Rajashree Tri Datta

We introduce an algorithm (Watta), which automatically calculates supraglacial lake bathymmetry and potential ice layers along tracks of the ICESat-2 laser altimeter. Watta uses photon heights estimated by the ICESat-2 ATL03 product and extracts supraglacial lake surface, bottom, corrected depth and (sub)surface ice cover in addition to producing surface heights at the native resolution of the ATL03 photon cloud. These measurements are used to constrain empirical estimates of lake depth from satellite imagery, which were thus far dependent on sparse sets of in-situ measurements for calibration. Imagery sources include Landsat OLI, Sentinel-2 and high-resolution Planet Labs PlanetScope and SkySat data, used here for the first time to calculate supraglacial lake depths.

The Watta algorithm was developed and tested using a set of 46 lakes near Sermeq Kujalleq (Jakobshavn) glacier in Western Greenland, and we use multiple imagery sources to assess the use of the red vs green band to extrapolate depths along a profile to full lake volumes. We use Watta-derived estimates in conjunction with high-resolution imagery from both satellite-based sources (tasked over the season) and nearly-simultaneous Operation IceBridge CAMBOT imagery (on a single airborne flight) for a focused study of the drainage of a single lake over the 2019 melt season.   Our results suggest that the use of multiple imagery sources (both publicly-available and commercial) in combination with altimetry-based depths, can move towards capturing the evolution of supraglacial hydrology at improved spatial and temporal scales.

How to cite: Wouters, B. and Datta, R. T.: Supraglacial lake bathymetry automatically derived from ICESat-2 constraining lake depth estimates from multi-source satellite imagery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10388, https://doi.org/10.5194/egusphere-egu21-10388, 2021.

09:16–09:18
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EGU21-10980
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ECS
Guy D. Tallentire, Jeff Evans, and Richard Hodgkins

The Arctic is warming at a rate of at least twice the global average. This is directly impacting upon the hydrological cycle; changing the balance of rain and snowfall, increasing losses of snow and glacier cover, and subsequently shifting the volumes and timing of meltwater runoff to nearby fjords and oceans. Sediment-laden meltwater plumes which are easily observable using satellite remote sensing, are good proxies for glacier runoff, both from subaerial rivers draining land-terminating glaciers, and subglacial discharge at tidewater glacier systems; they to bridge the gap between infrequent field observations and regular satellite data acquisitions. In-situ surface reflectance and surface water measurements were collected in July 2019, at the terrestrial glacier-fed Bayelva river plume, and the Blomstrandbreen subglacial discharge plume. These in-situ measurements, combined with Moderate Imaging Spectroadiometer (MODIS) satellite data were used to calibrate a relationship between surface reflectance and suspended sediment concentration at the two sediment-laden meltwater plumes. Using these empirical relationships, we determined seasonal sediment flux by establishing the thickness of the plume layer through conductivity, temperature and depth (CTD) profiles. Additionally, we determined plume metrics (area, extent or planform morphology and distribution), by integrating CTD profiles and measurements of meltwater runoff and sediment collected at the Bayelva hydrometric gauge, along with modelled datasets. We find that the sediment-laden meltwater plumes are extremely sensitive to variable inputs of meltwater runoff, with distinct changes in plume morphometry and sediment concentrations occurring at various points throughout the melt season, evidenced clearly during the transition from snow to firn and glacier ice melt, and after episodic rainfall events. Future work will apply these empirical relationships to other satellite datasets (including Planet, Sentinel and Landsat) from the last 20 years to determine long-term changes in the  sediment-laden meltwater plume systems, including their wider effects on fjord hydrography, and glaciomarine sedimentary processes in response to climatically-induced changes in the hydrology of the glacier systems.

How to cite: Tallentire, G. D., Evans, J., and Hodgkins, R.: Sediment-laden meltwater plume variability in Kongsfjorden, Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10980, https://doi.org/10.5194/egusphere-egu21-10980, 2021.

09:18–09:20
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EGU21-11371
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ECS
Robert Storrar, Andrew Jones, Frances Butcher, Nico Dewald, Chris Clark, Cathy Delaney, David Evans, Emma Lewington, Stephen Livingstone, and Chris Stokes

Meltwater exerts an important influence on ice sheet dynamics and has attracted an increasing amount of attention over the last 20 years. However, the active subglacial environment remains difficult to study mainly due to its inaccessibility. Understanding of the dimensions, pattern, and extent of subglacial meltwater conduits at the ice sheet scale is limited to relatively sparse observations. We address this gap by using the geomorphological record of Quaternary ice sheets as a proxy to quantify the dimensions and pattern of subglacial conduits at the ice sheet scale. We present the results of a high-resolution (2 m), large sample (n>50,000) study of three-dimensional esker morphometry at sample locations in SW Finland and Nunavut, Canada. Detailed mapping of esker crestlines and outlines permits the quantification of a number of parameters, including: length, width, height, cross-sectional area, volume, sinuosity, cross-sectional symmetry, and uphill/downhill trends. Whilst the dimensions of eskers reflect depositional processes as well as simply the size of the parent conduit, they nevertheless offer a powerful tool for understanding the size and shape of meltwater conduits and the configuration of subglacial drainage systems across large areas (entire ice sheets), and over long periods of time (from years to thousands of years) in both high spatial and temporal resolution. The results may be used to: (1) inform numerical models of subglacial meltwater drainage, (2) inform process models of esker formation, and (3) provide a dataset of esker morphometry against which other features may be compared (e.g. sinuous ridges on Mars).

How to cite: Storrar, R., Jones, A., Butcher, F., Dewald, N., Clark, C., Delaney, C., Evans, D., Lewington, E., Livingstone, S., and Stokes, C.: Ice sheet scale subglacial meltwater conduit dimensions and processes: insights from 3D morphometry of a large sample of eskers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11371, https://doi.org/10.5194/egusphere-egu21-11371, 2021.

09:20–09:22
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EGU21-13089
Florent Gimbert, Benoit Urruty, Philippe Roux, Adrien Gilbert, Ugo Nanni, and Albanne Lecointre

Crevasses are inherent features of glaciers and Ice Sheets. They exert a primary control on glacier dynamics, such as, for example, along shear margins through reducing the overall glacier ice viscosity, or at glacier and Ice Sheet fronts through controlling the onset of serac falls and of ice sheet instabilities (calving, ice shelf disintegration). However, our understanding of crevasse formation and propagation, and in particular the effect of melt water, remains limited due to lacking observations. Here we provide novel observational insights into englacial fracturing, the depth of crevasses and their depth propagation rates using dense seismic array monitoring on an Alpine glacier. We systematically detect and locate englacial seismic events through applying matched-field-processing on a particularly dense seismic array of 98 sensors deployed on the Glacier d’Argentière during 1-month in spring 2018. We observe rupture fronts along crevasses, which propagate from the glacier center to the glacier side at typical velocities of few hundreds of meters per day, i.e. at velocities that are much lower than those of seismic waves but much higher than those of glacier flow. We argue based on a dedicated spatial and temporal analysis that crevasse rupture propagation is set by the migration of water along the crevasse tip. We also observe that crevasses are associated with a wide range of depths, varying from the near surface to the glacier base, which at the present site is located about a hundred meters below the surface. This observation is particularly interesting, since it provides evidences that (i) crevasses are water filled and (ii) crevasses play a role in the supply of water to the bed. These findings are further supported by the observation that surface melt modulates the seismic activity of crevasses including those reaching the bed. Finally, by evaluating coherent structures in the crevasse population, we are able to infer their depth propagation rate, which we find is constant through the ice column, as expected if the surrounding ice stress field is counterbalanced by the water pressure in the crevasse. These observationally-derived findings provide useful grounds to test and improve theories of crevasse dynamics and their control in the overall transfer of water from the surface to the bed.

How to cite: Gimbert, F., Urruty, B., Roux, P., Gilbert, A., Nanni, U., and Lecointre, A.: Evidences of melt water control on crevasse propagation using dense array seismic observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13089, https://doi.org/10.5194/egusphere-egu21-13089, 2021.

09:22–09:24
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EGU21-14157
Roland Warner, Helen Fricker, Susheel Adusumilli, Philipp Arndt, Jonathan Kingslake, and Julian Spergel

Surface meltwater accumulating on Antarctica’s floating ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to enhanced ice discharge from the continent. Surface melting in Antarctica is predicted to increase significantly during coming decades, but the implications for ice shelf stability are unknown. We are still learning how meltwater forms, flows and alters the surface, and that rapid water-driven changes are not limited to summer. The southern Amery Ice Shelf in East Antarctica already has an extensive surface meltwater system and provides us with an opportunity to study melt processes in detail. We present high-resolution satellite data (imagery, ICESat-2 altimetry and elevation models from WorldView stereo-photogrammetry) revealing an abrupt change extending across ~60 km2 of the ice shelf surface in June 2019 (midwinter). We interpret this as drainage of an englacial lake through to the ocean below in less than three days. This left an uneven depression in the ice shelf surface, 11 km2 in area and as much as 80 m deep, with a bed of fractured ice: an “ice doline”. The englacial lake had lain beneath the perennially ice-covered portion of a 20 km2 meltwater lake. The reduced mass loading on the floating ice shelf after the drainage event resulted in flexure, with uplift of up to 36 m around the former lake. Applying an elastic flexural model to the uplift profiles suggests the loss of 0.75 km3 of water to the ocean. In summer 2020, we observed meltwater accumulating in a new lake basin created by the flexure. ICESat-2 observations profiled a new narrow meltwater channel (20 m wide and 3 m deep), rapidly incised inside the doline as meltwater spilled over from the new lake and started refilling the depression. This study demonstrates how high-resolution geodetic measurements from ICESat-2 and WorldView can explore critical fine-scale ice shelf processes. The insights gained will greatly improve our ability to model these processes, ultimately improving the accuracy of our projections.

How to cite: Warner, R., Fricker, H., Adusumilli, S., Arndt, P., Kingslake, J., and Spergel, J.: Rapid formation of an ice doline on Amery Ice Shelf, East Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14157, https://doi.org/10.5194/egusphere-egu21-14157, 2021.

09:24–09:26
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EGU21-14383
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ECS
Prateek Gantayat, Amber Leeson, James Lea, Noel Gourmelen, and Xavier Fettweis

The dynamics of the Greenland Ice Sheet (GrIS) is greatly affected by surface meltwater that is routed from the surface to the bed, for example when a supraglacial lake (SGL) drains. The South-West Greenland Ice Sheet (SWGrIS) has an abundance of such lakes that form and decay over every hydrological year. In case a crevasse is opened up underneath an SGL, the lake water is likely to drain via the crevasse into the ice-sheet’s bed. This in turn influences the ice sheet motion by increasing the lubrication at the ice-sheet’s base. SGLs may also either drain laterally via a supra-glacial meltwater channel or the water they contain can stay put throughout the hydrological year, refreezing in the winter. These processes may affect the ice rheology in addition to influencing ice flow. While simulating the future evolution of the GrIS, it is thus important to account for processes associated with the evolution of SGLs. Until now, however, none of the existing ice sheet models have fully accounted for these processes, in part because no hydrological model yet includes them all. Here we propose a new process-based hydrological model for the SWGrIS which fully accounts for the evolution of  SGLs. The model consists of four units. The first is a surface water routing unit where the daily-generated surface meltwater is routed assuming steepest decent into the surface depressions forming SGLs. The second unit uses principles of Linear Elastic Fracture Mechanics (LEFM) to deal with the scenario where an SGL drains into the bed through an underlying crevasse. The third deals with the SGL drainage event that occurs when a surface meltwater channel gets incised though the ice sheet’s surface due to erosion from the SGL’s overflowing meltwater i.e. channel incision. Finally, the fourth unit simulates the freezing/unfreezing of SGLs by calculating the energy balance at the SGL’s surface. Using this model forced by Modèle Atmosphérique Régionale (MAR) derived daily surface melt-water values we quantify a) the amount and location of surface meltwater injection to the ice-sheet’s bed via moulins or crevasses and ,b) the meltwater that is either  retained in SGL or drained overland via meltwater channels and stored elsewhere over the period 2011-2020, in the Leverett glacier catchment. In the future, we plan to integrate this hydrological model with the sophisticated state-of-the-art BISICLES ice sheet model.

How to cite: Gantayat, P., Leeson, A., Lea, J., Gourmelen, N., and Fettweis, X.: Simulating the formation and decay of supraglacial lakes in South-West Greenland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14383, https://doi.org/10.5194/egusphere-egu21-14383, 2021.

09:26–09:28
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EGU21-14890
Bernd Kulessa, Sarah Thompson, Sue Cook, Glenn Jones, Christopher Watson, Christian Schoof, and Victoria Lane

Large swathes of the margin of the East Antarctic Ice Sheet experience pronounced surface melting during the austral summer. The nature and temporal evolution of evolving surface hydrological systems are poorly known, however, as are their potential connections with englacial and subglacial water systems and their effects on ice dynamics. We have acquired helicopter-based ground-penetrating radar (GPR), electrical self-potential (SP), broadband passive seismic and GNSS data to delineate the geometry and monitor the temporal evolution of the subsurface hydrological system of the marine-terminating Sørsdal Glacier, Princess Elizabeth Land, East Antarctica, between the austral summers of 2017-18 and 2018-19. Our data reveal the presence of a shallow englacial hydrological system that is connected to surface lakes upstream of the grounding line and, surprisingly, is active not only in the austral summer but also through the Antarctic winter. Here we illustrate the spatial and temporal characteristics of the englacial hydrological system and its susceptibility to tidal forcing through the Antarctic winter. Our observations are consistent with persistent year-round redistribution of mass from grounded to floating portions of at the East Antarctic margin, with far-reaching consequences for ice shelf stability.

How to cite: Kulessa, B., Thompson, S., Cook, S., Jones, G., Watson, C., Schoof, C., and Lane, V.: Airborne and ground-based geophysical evaluation of the surface and englacial hydrological system of the Sørsdal Glacier, East Antarctica, and implications for ice-shelf stability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14890, https://doi.org/10.5194/egusphere-egu21-14890, 2021.

09:28–09:30
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EGU21-14907
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ECS
Elise Kazmierczak, Sainan Sun, and Frank Pattyn

Sliding laws determine to a large extent the sensitivity of the Antarctic ice sheet on centennial time scales (Pattyn, 2017, Bulthuis et al, 2019, Sun et al, 2020). Especially the contrast between linear and plastic sliding laws makes the latter far more responsive to changes at the grounding line. However, most studies neglect subglacial processes linked to those sliding laws. Subglacial hydrology may also play a role in modulating the amplitude of the reaction of marine ice sheets to forcing. Subglacial processes influence the effective pressure at the base. For a hard bed system, the latter can be defined by the ice overburden pressure minus the subglacial water pressure determined by routing of subglacial meltwater through a thin film. For soft-bed systems, the effective pressure is determined from till properties and physics. Here we investigate a wide range of subglacial processes and hydrology used in ice sheet models and implemented them in one ice sheet model (f.ETISh).

 

The subglacial hydrology models and till deformation models are coupled to different sliding and friction laws (linear, power law, Coulomb), leading to 24 different representations. The Antarctic ice sheet model was then forced by the ISMIP6 forcing in surface mass balance and ocean temperature until 2100 for different RCP scenarios (Seroussi et al., 2020). Furthermore, to sample the intrinsic sensitivity we performed the ABUMIP experiments (Sun et al., 2020) for the full set of subglacial characteristics.  Results demonstrate that the type of sliding law is the most determining factor in the sensitivity of the ice sheet, modulated by the subglacial hydrology.

How to cite: Kazmierczak, E., Sun, S., and Pattyn, F.: Subglacial hydrology modulates basal sliding response to climate forcing of the Antarctic ice sheet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14907, https://doi.org/10.5194/egusphere-egu21-14907, 2021.

09:30–09:32
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EGU21-14932
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ECS
Thomas Barnes, Amber Leeson, Mal McMillan, Vincent Verjans, and Chris Kittel

In 2020, 11.8% of northern George VI ice shelf was covered by supraglacial lakes, and it has been speculated that this was a record high lake density. Supraglacial lakes are associated with ice shelf instability, and were implicated in the collapse of Larsen B in 2002, where ~10% lake density was recorded. Here we use optical satellite imagery from Sentinel-2 and Landsat-1-8 in combination with recorded and modelled climate data from Fossil Bluff AWS, the MAR climate model, and the community firn model to study lakes on George VI ice shelf between 1973 and 2020. We find that the high density of lakes in 2020 was not unique, with similar events occurring five times in the study period, including a record value of 12.1% density in 1989. Furthermore, we find lake density to be controlled by a combination of high firn air content, high air temperature and a neutral southern annular mode, thus a strong melt year alone is insufficient for producing high lake densities. 2020 had record-high melt and temperature values, which suggests that this should also be a record year for lake coverage. A thicker than usual snow/firn pack in the winter prior to the 2020 melt season however, had a dampening effect on lake formation and thus lakes were less abundant than in 1989. As temperatures at this location are projected to increase in coming decades, but snowfall is expected to stay the same, future high melt years are very likely to lead to new record high lake coverage. Since supraglacial lakes are an indicator of ice shelf stability, this suggests that George VI may be rendered unstable within our lifetime.

How to cite: Barnes, T., Leeson, A., McMillan, M., Verjans, V., and Kittel, C.: Supraglacial Lakes on George VI Ice Shelf from a multi-decadal perspective, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14932, https://doi.org/10.5194/egusphere-egu21-14932, 2021.

09:32–09:34
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EGU21-16349
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ECS
Rebecca Dell, Alison Banwell, Neil Arnold, Ian Willis, Anna Ruth W. Halberstadt, Tom Chudley, and Hamish Pritchard

Supraglacial melt is observed across the majority of Antarctic ice shelves and is expected to increase in line with rising air temperatures. Surface meltwater may run off the ice shelf edge and into the ocean, or be stored within firn pore spaces (slush) and supraglacial water bodies (ponds, lakes or streams). When stored either as slush or supraglacial water bodies, the water can indirectly impact ice shelf dynamics, and potentially facilitate ice shelf collapse. Numerous studies have quantified ice shelf meltwater in supraglacial water bodies, however, despite its importance, no studies exist that quantify the extent of slush on a pan-Antarctic scale.

Here, we develop a supervised classifier in Google Earth Engine capable of identifying both slush and ponded water on a pan-Antarctic scale using Landsat 8 imagery. We train and test our classifier on six ice shelves: (1) Nivlisen, (2) Roi Baudouin, (3) Amery, (4) Shackleton, (5) Nansen, (6) George VI. A k-means clustering algorithm is applied to selected Landsat 8 training scenes, and the output clusters are manually interpreted to form training classes (i.e. slush, water, and other surface types (e.g. blue ice, dirty ice)). These training classes are then used to train a Random Forest Classifier, and the accuracy of the outputs are assessed using expert elicitation. Overall, the classifier accuracy for water and slush is 78 % and 70 % respectively. The validated classifier is then applied to numerous ice shelves across Antarctica, in order to produce estimates of slush and water extent from 2013 to the present day.

How to cite: Dell, R., Banwell, A., Arnold, N., Willis, I., Halberstadt, A. R. W., Chudley, T., and Pritchard, H.: A record of slush and water extent on Antarctic ice shelves from 2013 to present day, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16349, https://doi.org/10.5194/egusphere-egu21-16349, 2021.

09:34–10:30